Play ios audio device while recording

I was instructed to add VOIP to the game (cross-platform, so I cannot use Apple gakit for this).

For 3 or 4 days, I try to wrap my head around an audio unit and remoteIO ... I have missed dozens of examples, etc., but each time it uses a simple algorithm to input PCM and plays it on the speaker. According to Apple documentation, to do VOIP, we have to use kAudioSessionCategory_PlayAndRecord.

UInt32 audioCategory = kAudioSessionCategory_PlayAndRecord;

        status = AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, 
                                         sizeof(audioCategory), 
                                         &audioCategory);
        XThrowIfError(status, "couldn't set audio category");

1) But it seems to me that playAndRecord will always play what comes from the microphone (or, more importantly, the PerformThru // aurioTouch callback ), am I wrong?

I have the easiest callback without doing anything except AURender

static OSStatus PerformThru(
                            void                        *inRefCon, 
                            AudioUnitRenderActionFlags  *ioActionFlags, 
                            const AudioTimeStamp        *inTimeStamp, 
                            UInt32                      inBusNumber, 
                            UInt32                      inNumberFrames, 
                            AudioBufferList             *ioData)
{
OSStatus err = AudioUnitRender(THIS->rioUnit, ioActionFlags, inTimeStamp, 1, inNumberFrames, ioData);
    if (err) 
       printf("PerformThru: error %d\n", (int)err);
    return err
}

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